During integrated circuit fabrication, one or more chemical-mechanical polishing (CMP) processes may be utilized to form planar surfaces for a semiconductor device structure. In a conventional CMP process, a material having a non-planar topography is contacted with a rotating polishing pad in the presence of a polishing slurry. The polishing slurry includes a chemically reactive material and an abrasive material (e.g., silica, alumina, ceria, etc.). The chemically reactive material chemically modifies at least some of the material to promote removal of the material by the abrasive material and the rotating polishing pad, and may also remove some of the material. The abrasive material and the rotating polishing pad physically modify and remove at least some portions of the material not removed by the chemically reactive material.
The efficiency of a CMP process depends largely on the ability of the CMP process to remove elevated regions of the material faster than recessed regions of the material. Removing the elevated regions of the material faster than the recessed regions of the material reduces the amount of the material that must initially be present to form a planar surface, and reduces the risk of dishing. Accordingly, it is generally desirable to remove elevated regions of the material without substantially reducing a thickness of the recessed regions of the material.
One method commonly utilized to remove elevated regions of a material faster than recessed regions of the material includes incorporating protective additives (e.g., polymers, surfactants, etc.) into the polishing slurry. During the CMP process, the protective additives weakly adhere to the surfaces of the material, allowing the protective additives to be easily removed from the elevated regions of the material while providing some protection to the recessed regions of the material. However, as with the elevated regions of the material, the polishing pad and the abrasive material of the polishing slurry can remove the weakly adhered protective additives from the recessed regions of the material, limiting the protection provided by the protective additives. For example, physical removal of protective additives from recessed regions of the material frequently occurs when the recessed regions of the material are relatively large (e.g., have a lateral dimension of greater than or equal to about 0.5 micrometer).
Another method commonly utilized to remove elevated regions of a material faster than recessed regions of the material includes forming a continuous, solid film over the surfaces of the material prior to performing the CMP process. The solid film strongly adheres to the surfaces of the material, and is generally substantially non-reactive with the etchant of the polishing slurry. Consequently, the solid film can substantially limit or prevent removal of the recessed regions of the material. However, such methods can be complex and costly, requiring multiple processing acts and/or multiple processing materials. For example, after forming the solid film, an initial CMP process (e.g., including a polishing slurry selective to the solid film) can be used to remove portions of the solid film on the elevated regions of the material, followed by another CMP process (e.g., including a different polishing slurry selective to the material) to remove the elevated regions of the material, followed by yet another CMP process to remove the solid film on the recessed regions of the material. In addition, as the solid film is strongly adhered to the surfaces of the material, removing the solid film may require significant downward force, applying undesirable stress on the relatively fragile semiconductor device structure.
Yet another method commonly utilized to remove elevated regions of a material faster than recessed regions of the material includes embedding at least some of the abrasive particles to be used in the polishing slurry in the rotating polishing pad. During the CMP process, the abrasive particles embedded in the rotating polishing pad are released in a controlled manner to gradually remove the elevated regions of the material while limiting removal of the recessed regions of the material. However, such methods can have limited applicability at least due to material selectivity challenges, and can have an undesirably slow material removal rate.
It would, therefore, be desirable to have an improved method of forming a planar surface for a semiconductor device structure to overcome one or more of the above problems.